This type of vehicle seat includes a seat pad forming an outer shape of the seat and a seat cover covering an outer surface of the seat pad, and a design surface of the seat is configured by the seat cover. The seat cover is formed by sewing a plurality of cover pieces, and a seam at which the cover pieces are sewn to each other extends in a predetermined direction. That is, the seat cover is provided with a sewn portion at which seam allowances of a pair of adjacent cover pieces are overlapped in a state where front surfaces thereof face each other. Further, in the sewn portion, the seam allowances are sewn at the seam, and the seam is arranged between a pair of cover pieces and extends in a predetermined direction. Further, in the seat cover covering the outer surface of the seat pad, each cover piece is deployed in a planar shape with the sewn portion serving as a base point, so as to configure the design surface, and the sewn portion is arranged on a back side of the design surface. From the viewpoint of avoiding meandering or folding of the seam, the sewn portion is arranged on the seat pad in a state of being tilted in a constant direction.
For example, in a seat cover disclosed in EP 3103678 A1, a pair of cover pieces is deployed in a planar shape with a sewn portion serving as a base point, so as to configure a design surface, and the sewn portion is arranged on a back side of the design surface. Further, on a back side of the seat cover, a planar regulating member is attached along the back surface of the seat cover, and the regulating member stretches the sewn portion so as to tilt the sewn portion in a constant direction. In the sewn portion of such a state, an end portion including a seam allowance of one of the cover pieces is curved, with the sewn portion serving as a base point, to form a lateral U shape on a transverse section thereof, and a seam allowance of the other cover piece is overlapped on a lower side of the end portion. Since the end portion of the one cover piece curved into the lateral U shape is overlapped with the seam allowance of the other cover piece, a wall thickness of the sewn portion in the tilted state becomes thick than other parts of the seat cover.
Incidentally, in this type of vehicle seat, there is a demand for matching a shape of the outer surface of the seat pad and a shape of the design surface of the seat cover as much as possible, from a viewpoint of improving shape reproducibility of the seat. However, since the sewn portion is relatively thicker in the known technique, the seat cover tends to be raised partially due to the sewn portion. For example, the outer surface of the seat pad may be partially curved from the viewpoint of improving the design of the seat. Further, when the sewn portion is arranged on a region forming the curved surface of the seat pad, there is a possibility that the seat cover may be raised excessively due to circumferential length difference between the front and back of the sewn portion, or the like. For this reason, the configuration of the known technique cannot be adopted smoothly from the viewpoint of improving the shape reproducibility of the seat, or the like.